JSFiddle - React, Tailwind, and code Playground

HTML

<div id='content'>
    <textarea placeholder='resizing me should trigger mutations? no?'></textarea>
</div>
<div>
    <button>This JS works fine. Mutation is recorded</button>
</div>

SCSS

#content{
    background-color: rgb(175, 199, 221);
    display: inline-block;
}
textarea{
}

JavaScript

var target = document.querySelector('#content');
 
var observer = new MutationObserver(function(mutations) {
  console.log(mutations);   
});
 
var config = { attributes: true, childList: true, characterData: true };
observer.observe(target, config);

document.querySelector('button').addEventListener('click',function(){
    target.style.height = '200px';
});